1. Field
The disclosed concept pertains generally to electric vehicle supply equipment and, more particularly, to testing apparatus for such electric vehicle supply equipment.
2. Background Information
An electric vehicle (EV) charging station, also called an EV charging station, electric recharging point, charging point, and EVSE (Electric Vehicle Supply Equipment), is an element in an infrastructure that supplies electric energy for the recharging of electric vehicles, plug-in hybrid electric-gasoline vehicles, or semi-static and mobile electrical units such as exhibition stands.
An EV charging station is device that safely allows electricity to flow. These charging stations and the protocols established to create them are known as EVSE, and they enhance safety by enabling two-way communication between the charging station and the electric vehicle.
The 1996 NEC and California Article 625 define EVSE as being the conductors, including the ungrounded, grounded, and equipment grounding conductors, the electric vehicle connectors, attachment plugs, and all other fittings, devices, power outlets or apparatus installed specifically for the purpose of delivering energy from premises wiring to an electric vehicle.
EVSE is defined by the Society of Automotive Engineers (SAE) recommended practice J1772 and the National Fire Protection Association (NFPA) National Electric Code (NEC) Article 625. While the NEC defines several safety requirements, J1772 defines the physical conductive connection type, five pin functions (i.e., two power pins (Hot1 and Hot2 or neutral), one ground pin, one control pilot pin, and one proximity pin), the EVSE to EV handshake over the pilot pin, and how both parts (EVSE and EV) are supposed to function. Currently, however, EVSE does not have a mechanism to check its proper function without an EV present to test the function of the EVSE and complete the J1772 pilot circuit.
Two-way communication seeks to ensure that the current passed to the EV is both below the limits of the EV charging station itself and below the limits of what the EV can receive. There are additional safety features, such as a safety lock-out, that does not allow current to flow from the EV charging station until the EV connector or EV plug is physically inserted into the EV and the EV is ready to accept energy.
J1772 in North America and IEC 61851 standard use a very simple but effective pilot circuit and handshake in the EVSE. For charging a vehicle using alternating current (AC), basically a signal is generated on the pilot pin 4 of FIG. 1, 12 Vdc open circuit when measured to ground pin 3. When the EVSE cable and connector 10 is plugged into an EV inlet 11 of a compliant vehicle 12, the vehicle's circuit has a resistor 14 and a diode 16 in series that ties to ground 18 in order to drop the 12 Vdc to 9 Vdc. After the EVSE 20 sees this drop in voltage, it turns on a pulse-width modulated (PWM) generator 22 that defines the maximum available line current (ALC) on the charging circuit. The vehicle charge controller 24 reads the percentage of the duty cycle of the PWM signal, which is equivalent to a certain amperage, and sets the maximum current draw on the onboard vehicle rectifier/charger 26, in order to not trip an upstream circuit interrupter (not shown). The vehicle 12, in turn, adds another resistor 28 in parallel with the resistor 14 of the vehicle's resistor and diode 14,16 series combination, which then drops the top level of the PWM pilot signal to 6 Vdc. This tells the EVSE 20 that the vehicle 12 is ready to charge. In response, the EVSE 20 closes an internal relay/contactor 30 to allow AC power to flow to the vehicle 12.
It is believed that manufacturers of EVSE, understanding J1772, have built test boxes to simulate the function of an EV to test EVSE during development, since vehicles are scarce and relatively very expensive compared to charging equipment. These test boxes allow for testing that the EVSE is functioning properly by simulating the circuit on board the EV. However, these simple test fixtures are separate, portable devices (representing the vehicle) and they are simply designed to check functionality and compliance of the EVSE.
There is room for improvement in electric vehicle supply equipment testing apparatus.